Sintered NdFeB is an anisotropic magnet produced by powder sintering. Generally, only blanks can be produced after sintering, and then they can be made into magnets of various shapes after mechanical processing (such as wire cutting, slicing, grinding, etc.). Sintering of sintered NdFeB refers to the process of heating the green body to a temperature below the melting point of the powder matrix phase and keeping it warm for a period of time in order to further improve the performance and usability of the magnet, improve the contact properties between powders, increase strength, and make the magnet have high-performance microstructural characteristics.

Sintering is an important process in sintered NdFeB, and it is valued by manufacturers and researchers. The relative density of NdFeB powder compacts is generally 50% to 70%, and the porosity is generally 30% to 50%. The bonding between particles is all mechanical bonding, and the bonding strength is low. If the molding pressure is very high, some of the particles that have been in contact with each other have already produced elastic or plastic deformation. At this time, the sample is more likely to crack, and its microstructure is not enough to produce high magnetic properties.

During the sintering process of NdFeB green body, a series of physical and chemical changes will occur. First, the gas (including water vapor) adsorbed on the surface of the powder particles is removed, the organic matter (such as oil that may be stained during isostatic pressing or added antioxidants and lubricants, etc.) evaporates and volatilizes, stress is eliminated, the oxides on the surface of the powder particles are reduced, and the deformed powder particles recover and recrystallize.

Secondly, atomic diffusion, material migration, the contact between particles changes from mechanical contact to physical and chemical contact, forming a combination of metal bonds and covalent bonds. The contact surface between the powders is expanded, and a sintering neck appears, followed by the growth of the sintering neck, the increase in density, and the growth of grains.

The porosity of the powder green body is large, the surface area is also large, so the surface energy is also large, and it also has lattice distortion energy, which makes the powder green body as a whole in a high-energy state. From an energy point of view, this is unstable and has a tendency and driving force to spontaneously sinter and bond into a dense body.

Therefore, under certain temperature conditions, that is, when dynamics allow, the contact between powder particles will change from point to surface in order to reduce the surface area and surface energy. As the contact surface between particles expands, the green body begins to shrink and densify, becoming a sintered body. In short, sintering is the process of changing the powder body from a green body to a blank.

Sintered NdFeB permanent magnet materials have excellent magnetic properties and are widely used in electronics, power machinery, medical equipment, toys, packaging, hardware machinery, aerospace and other fields. The more common ones are permanent magnet motors, speakers, magnetic separators, computer disk drives, magnetic resonance imaging equipment and instruments, etc.